Fabric of continuous graphene fiber yarns from functionalized graphene sheets

ABSTRACT

Provided is a fabric comprising a layer of yarns combined (by weaving, braiding, knitting, or non-woven) to form the fabric wherein the yarns comprise one or a plurality of graphene-based long or continuous fibers. The long or continuous fiber comprises chemically functionalized graphene sheets that are chemically bonded with one another having an inter-planar spacing d 002  from 0.36 nm to 1.5 nm as determined by X-ray diffraction and a non-carbon element content of 0.1% to 40% by weight, wherein the functionalized graphene sheets are substantially parallel to one another and parallel to the fiber axis direction and the fiber contains no core-shell structure, have no helically arranged graphene domains, and have a length no less than 0.5 cm and a physical density from 1.5 to 2.25 g/cm 3 . The graphene fiber typically has a thermal conductivity from 300 to 1,600 W/mK, an electrical conductivity from 600 to 15,000 S/cm, or a tensile strength higher than 1.0 GPa.

FIELD OF THE INVENTION

The present invention relates generally to the field of graphene fiberyarns and fabrics and, more particularly, to a new class of fabriccontaining continuous graphene fibers produced from functionalizedgraphene sheets. This new class of fibers, yarns, and fabrics exhibits acombination of exceptionally high tensile strength, elastic modulus,thermal conductivity, and electrical conductivity.

BACKGROUND OF THE INVENTION

Continuous carbon fibers and graphite fibers are produced from pitch,polyacrylonitrile (PAN), and rayon. Most carbon fibers (about 90%) aremade from PAN fibers. A small amount (about 10%) is manufactured frompetroleum pitch or rayon. Although the production of carbon fibers fromdifferent precursors requires different processing conditions, theessential features are very similar. Generally, carbon fibers aremanufactured by a controlled pyrolysis of stabilized precursor fibers.Precursor fibers (e.g. PAN) are first stabilized at about 200-400° C. inair by an oxidization process. The resulting infusible, stabilizedfibers are then subjected to a high temperature treatment atapproximately 1,000-1,500° C. (up to 2,000° C. in some cases) in aninert atmosphere to remove hydrogen, oxygen, nitrogen, and othernon-carbon elements. This step is often called carbonization and it cantake 2-24 hours to complete, depending upon the carbonizationtemperature and the starting material used. Carbonized fibers can befurther graphitized at an even higher temperature, up to around 3,000°C. to achieve higher carbon content and higher degree of graphitization,mainly for the purpose of achieving higher Young's modulus or higherstrength in the fiber direction. This takes another 1-4 hours understrictly controlled atmosphere and ultra-high temperature conditions.The properties of the resulting carbon/graphite fibers are affected bymany factors, such as crystallinity, crystallite sizes, molecularorientation, carbon content, and the type and amount of defects.

Specifically, the carbon fibers can be heat-treated to become highmodulus graphite fibers (from pitch) or high strength carbon fibers(from PAN-based). Carbon fibers heated in the range from 1500-2000° C.(carbonization) exhibits the highest tensile strength (5,650 MPa), whilecarbon fiber heated from 2500 to 3000° C. (graphitizing) exhibits ahigher modulus of elasticity (531 GPa). The tensile strength ofcarbon/graphite fibers is typically in the range from 1-6 GPa, and theYoung's modulus is typically in the range from 100-588 GPa.

Broadly speaking, in terms of final mechanical properties,carbon/graphite fibers can be roughly classified into ultra-high modulus(>500 GPa), high modulus (>300 GPa), intermediate modulus (>200 GPa),low modulus (100 GPa), and high strength (>4 GPa) carbon fibers. Carbonfibers can also be classified, based on final heat treatmenttemperatures, into type I (2,000° C. heat treatment), type II (1,500° C.heat treatment), and type III (1,000° C. heat treatment). Type IIPAN-based carbon fibers are usually high strength carbon fibers, whilemost of the high modulus carbon fibers belong to type I from pitch.

Regardless the type of carbon fibers or graphite fibers desired, theproduction of continuous carbon fibers and graphite fibers from pitch,PAN, and rayon is a tedious, energy-intensive, very challenging(requiring extreme temperature and atmosphere control), and expensiveprocess. A strong need exists for a facile, less energy-intensive,simpler and more scalable, and more cost-effective process for producingadvanced fibers.

Carbon is known to have five unique crystalline structures, includingdiamond, fullerene (0-D nano graphitic material), carbon nanotube orcarbon nanofiber (1-D nano graphitic material), graphene (2-D nanographitic material), and graphite (3-D graphitic material, includinggraphite fiber). The carbon nanotube (CNT) refers to a tubular structuregrown with a single wall or multi-wall. Carbon nanotubes (CNTs) andcarbon nanofibers (CNFs) have a diameter on the order of a fewnanometers to a few hundred nanometers. Their longitudinal, hollowstructures impart unique mechanical, electrical and chemical propertiesto the material. The CNT or CNF is a one-dimensional nanocarbon or 1-Dnano graphite material. Although multiple CNTs or CNFs can be spun intofiber yarns, these yarns are not considered as “continuous fibers”. Theyare twisted aggregates of individual CNTs or CNFs (each being but a fewmicrons long) that are not self-bonded together; instead, they aremechanically fastened together as a yarn.

Bulk natural graphite is a 3-D graphitic material with each particlebeing composed of multiple grains (a grain being a graphite singlecrystal or crystallite) with grain boundaries (amorphous or defectzones) demarcating neighboring graphite single crystals. Each grain iscomposed of multiple graphene planes that are oriented parallel to oneanother. A graphene plane in a graphite crystallite is composed ofcarbon atoms occupying a two-dimensional, hexagonal lattice. In a givengrain or single crystal, the graphene planes are stacked and bonded viavan der Waal forces in the crystallographic c-direction (perpendicularto the graphene plane or basal plane). Although all the graphene planesin one grain are parallel to one another, typically the graphene planesin one grain and the graphene planes in an adjacent grain are differentin orientation. In other words, the orientations of the various grainsin a graphite particle typically differ from one grain to another.

A graphite single crystal (crystallite) per se is anisotropic with aproperty measured along a direction in the basal plane (crystallographica- or b-axis direction) being dramatically different than if measuredalong the crystallographic c-axis direction (thickness direction). Forinstance, the thermal conductivity of a graphite single crystal can beup to approximately 1,920 W/mK (theoretical) or 1,800 W/mK(experimental) in the basal plane (crystallographic a- and b-axisdirections), but that along the crystallographic c-axis direction isless than 10 W/mK (typically less than 5 W/mK). Further, the multiplegrains or crystallites in a graphite particle are typically all orientedalong different directions. Consequently, a natural graphite particlecomposed of multiple grains of different orientations exhibits anaverage property less than 200 W/mK.

It would be highly desirable in many applications to produce a bulkgraphite-derived object or graphitic fiber having sufficiently largedimensions and having all graphene planes being essentially parallel toone another along one desired direction (e.g. along the fiber axis).

The constituent graphene planes of a graphite crystallite can beexfoliated and extracted or isolated from a graphite crystallite toobtain individual graphene sheets of carbon atoms provided theinter-planar van der Waals forces can be overcome. An isolated,individual graphene sheet of carbon atoms is commonly referred to assingle-layer graphene. A stack of multiple graphene planes bondedthrough van der Waals forces in the thickness direction with aninter-graphene plane spacing of 0.3354 nm is commonly referred to as amulti-layer graphene. A multi-layer graphene platelet has up to 300layers of graphene planes (<100 nm in thickness), but more typically upto 30 graphene planes (<10 nm in thickness), even more typically up to20 graphene planes (<7 nm in thickness), and most typically up to 10graphene planes (commonly referred to as few-layer graphene inscientific community). Single-layer graphene and multi-layer graphenesheets are collectively called “nano graphene platelets” (NGPs).Graphene sheets/platelets or NGPs are a new class of carbon nanomaterial(a 2-D nano carbon) that is distinct from the 0-D fullerene, the 1-DCNT, and the 3-D graphite.

Our research group pioneered the development of graphene materials asearly as 2002: (1) B. Z. Jang and W. C. Huang, “Nano-scaled GraphenePlates,” U.S. Pat. No. 7,071,258 (Jul. 4, 2006), application submittedon Oct. 21, 2002; (2) B. Z. Jang, et al. “Process for ProducingNano-scaled Graphene Plates,” U.S. patent application Ser. No.10/858,814 (Jun. 3, 2004) (U.S. Patent Pub. No. 2005/0271574); and (3)B. Z. Jang, A. Zhamu, and J. Guo, “Process for Producing Nano-scaledPlatelets and Nanocomposites,” U.S. patent application Ser. No.11/509,424 (Aug. 25, 2006) (U.S. Patent Pub. No. 2008-0048152).

In a recent report [Z. Xu & C. Gao, “Graphene chiral liquid crystals andmacroscopic assembled fibers,” Nature Communications, 2, 571 (2011)],graphene oxide sheets can form chiral liquid crystals in atwist-grain-boundary phase-like model with simultaneous lamellarordering and long-range helical frustrations. Aqueous graphene oxideliquid crystals can then be continuously spun into meters of macroscopicgraphene oxide fibers, which are chemically reduced to obtain RGOfibers. During the spinning process for GO fibers, the GO dispersionswere loaded into glass syringes and injected into the NaOH/methanolsolution under the conditions of 1.5 MPa N₂. The NaOH/methanol solutionis a coagulation solution (a non-solvent for GO) and the GO sheets areprecipitated out in a loosely connected, very low density fiber. Thefibers produced in the coagulation bath were then rolled onto a drum,washed by methanol to remove the salt, and dried for 24 hours at roomtemperature. The as-prepared GO fibers were then chemically reduced inthe aqueous solution of hydro-iodic acid (40%) at 80° C. for 8 hours,followed by washing with methanol and vacuum drying for 12 hours.

Clearly, this is a very tedious and time-consuming process. Further, theGO sheets must be dispersed in water to a critical extent that they formchiral liquid crystals with a twist-grain-boundary phase structure inthe GO suspension. This chiral or twist-grain boundary structure is afatal defect as far as the mechanical strength of macroscopic graphenefibers is concerned, as evidenced by the relatively low tensile strength(102 MPa) reported by Xu, et al. This is three orders of magnitude lowerthan the intrinsic strength (130 GPa) of individual graphene sheets.Another severe problem of this process is the notion that thespinning-coagulation procedure inherently results in highly porous andnon-oriented graphene sheets in the graphene fiber (e.g. FIG. 2(c) andFIG. 2(d)). This porous and non-parallel graphene structure is anotherreason responsible for such a low tensile strength and low Young'smodulus (5.4 GPa), which is almost three orders of magnitude lower thanthe theoretical Young's modulus of graphene (1,000 GPa).

A similar spinning-coagulation process was reported by Cong, et al [H.P. Cong, et al. “Wet-spinning assembly of continuous, neat, andmacroscopic graphene fibers,” Scientific Report, 2 (2012) 613; DOI:10.1038/srep00613]. Again, the reported tensile strength and Young'smodulus of the graphene fibers are very poor: 145 MPa and 4.2 GPa,respectively. Slightly better tensile strength (180 MPa) was observedwith graphene oxide fibers prepared by a confined-dimension hydrothermalmethod was reported [Z. Dong, et al. “Facile fabrication of light,flexible and multifunctional graphene fibers,” Adv. Mater. 24, 1856-1861(2012)]. Even after a thermal reduction treatment, the maximumachievable tensile strength was only 420 MPa. Again, the graphene sheetsin these graphene fibers, just like in the graphene fibers prepared byspinning-coagulation, remain discrete and poorly oriented. The fibersare also highly porous and of limited length. Furthermore, this processis not a scalable process and cannot be used to mass-produce continuousgraphene fibers.

In most of the practical applications, fibers and yarns are not thefinal utilization shape or form. A particularly useful form is fabric,which may be obtained by weaving, braiding, knitting, or by a non-wovenprocess. The properties of a fabric depend on the properties of thefibers. For illustration purposes, cotton or wool fibers are used tokeep a person warm in the winter, asbestos fibers are used as a flameretardant, carbon fibers for strength reinforcement, glass fibers forinsulation, metallic fibers for conducting electricity. Unfortunately,combining fibers does not always result in a fabric that possesses auseful set of properties for a range of applications. For example,anti-ballistic fibers, such as Kevlar, are sensitive to heat. Althoughadding flame retardant fibers may provide limited support, Kevlarfabrics would not work optimally as a projectile resistant material ifexposed to continuous heat. Ideally, compatible fibers having uniquemechanical, thermal, electrical, optical, and chemical properties wouldbe formed into fabrics that demonstrate all the desired propertieswithin the fabric. However, all the state-of-the-art fabrics have alimited range of applications due to the limited functional propertiesof their constituent fibers.

Fabric quality and functional performance depends on the ability tointer-weave yarns with one another. The material structure, size, andshape of the fibers and resulting yarns may become limiting factors forthe range of application of a certain fabric. For examples, fabrics thatblock entry of pathogenic agents require that the yarns of consistentquality be interwoven tightly to prevent any gaps between one another.The thickness and shapes of individual fibers alone could allowsignificant gaps within each yarn defined by those fibers. Generally,there are no available continuous fibers having a nanometerdiameter/thickness and shape that provide significant strength,ductility, geometric flexibility, and cross-sectional shape of a yarn soas to define a multi-functional fabric. There is an urgent need to havea new type of graphitic fibers that can be made into a multi-functionalfabric.

We have developed a graphene-based continuous or long fibers thatexhibit exceptional mechanical, electrical, and thermal properties. Weproceeded to further investigate the technical feasibility ofweaving/braiding these continuous graphene fibers into a fabric andexplore the potential utilization of such a fabric. These new graphenefibers are generally flat-shaped in cross-section (non-circular,non-ellipsoidal, and non-oval shape), with a large width (typically from0.01 μm to 20 μm and more typically from 0.1 μm to 10 μm, but readilyadjustable) and a small thickness (typically from 1 nm to 1 μm, readilyadjustable), hence a high width-to-thickness ratio (typically from 10 to1000). They are relatively solid and non-porous. These shapes,structures, and morphologies are in contrast to those of the graphenefibers produced by coagulation and spinning, which are helical andhighly porous in nature and have a chiral or twist-grain boundarystructure. The helical structure and high porosity level of theseconventional graphene fibers are a natural consequence of the liquidcrystal structure of the starting graphene oxide material and therequired precipitation of graphene from a liquid coagulation bath. Thegraphene fibers obtained by drawing CVD graphene films into a fibrousform are also highly porous. These pores and helices severely weakenthese conventional fibers, exhibiting dramatically lower elastic modulusand strength.

We have further observed that, due to the substantially rectangularcross-section of some of the presently invented continuous graphenefibers, the yarns containing multiple continuous fibers can have across-section that is rectangular or flat-shaped. When one combinesmultiple filaments together (e.g. of those conventional fibers with acircular cross-section or irregular-shape cross-section), there is alimit to the packing factor. The highest packing factor is typicallybetween 50% and 65% by volume even for circular-cross-section fibers. Incontrast, the presently invented rectangular or flat-shaped graphenefibers can be packed into a yarn with a packing factor close toessentially 100%. The packing factor can be adjusted to be between 20%and essentially 100%, for composite structure or filter applications. Apacking factor of 70-85% is particularly useful for compositeapplications. Our research data have demonstrated that the flexuralstrength and elastic modulus values of polymer matrix compositescontaining presently invented graphene fiber-based fabrics as areinforcement phase are significantly higher than those of thecomposites containing a comparable volume fraction of conventionalgraphitic fibers. Additionally, fabrics that block entry of pathogenicagents require that the yarns of highest packing factors be interwoventightly to prevent any gaps between one another. The thickness andshapes of conventional fibers alone could allow significant gaps withineach yarn defined by those fibers. The instant invention providestightly packed yarns and fabrics. These features are not achievable withconventional graphitic fibers.

It is an object of the present invention to provide yarns and fabricscontaining high-strength and high-modulus continuous graphene fibers byusing particles of natural graphite or artificial graphite as thestarting material for graphene sheet production. A specific object ofthe present invention is to provide a fabric that containsgraphene-derived continuous or long graphene fibers that are composed offunctionalized graphene sheets that are chemically bonded orinterconnected together, not just an aggregate of discrete graphenesheets. Another object of this invention is to provide a process forproducing such a graphene fabric.

SUMMARY OF THE INVENTION

The present invention provides a fabric comprising multiple yarnscombined to form the fabric, wherein at least one of said yarnscomprises one or a plurality of graphene-based long or continuousfibers. The graphene-based long or continuous fiber comprises chemicallyfunctionalized graphene sheets that are chemically bonded orinterconnected with one another having an inter-planar spacing d₀₀₂ from0.36 nm to 1.5 nm as determined by X-ray diffraction and a non-carbonelement content (e.g. H, O, N, B, P, Cl, F, Br, I, S, etc.) of 0.1% to47% by weight, wherein the functionalized graphene sheets aresubstantially parallel to one another (typically having a degree oforientation from 86% to 99%) and parallel to the fiber axis directionand the fiber contains no core-shell structure, have no helicallyarranged graphene domains, and have a length no less than 0.5 cm and aphysical density from 1.5 to 2.25 g/cm³. This long fiber can be anessentially “continuous fiber” wound as a spool on a roller and having alength up to several kilometers (e.g. 10 km). The graphene sheets aretypically interconnected with one another via chemical bonding orreactions between the chemically active functional groups attached torespective adjacent graphene sheets. These chemically active functionalgroups are capable of reacting with neighboring functional groups byforming covalent bonds, hydrogen bonds, and/or π-π bonds.

One interesting and unique characteristic of the presently inventedfabric is that the constituent fibers derived from functionalizedgraphene sheets can be made into a more-or-less rectangularcross-section (e.g. as schematically shown in FIG. 4(b)). As aconsequence, the yarns containing multiple continuous fibers can have across-section that is rectangular or flat-shaped. The fibers can becombined into a yarn having a packing factor >60% by volume (voidcontent <40% by volume). The packing factor can be and, typically, isgreater than 70% or even 80%. In principle, the rectangular fibers ofthe instant invention enable a yarn packing factor approaching 100% byvolume. Preferably, the yarns have a width-to-thickness ratio greaterthan 5, more preferably >20, and can be greater than 150. The fabric orthe yarn can have a thickness less than 1 μm, or even less than 100 nm.

The fabric, the yarn, or the graphene-based long or continuous fiber canhave a cross-section that is rectangular or flat-shaped, having a widthand a thickness. The fabric or a yarn may have a thickness as small asfrom 10 nm to 1 μm. A flat-shaped fiber or yarn has a cross-section witha width-to-thickness ratio of at least 2, preferably at least 3, morepreferably at least 5, but can be from 1.5 to 1,000. When one combinesmultiple conventional filaments together (e.g. those conventional fiberswith a circular cross-section or irregular-shape cross-section), thereis a limit to the packing factor. The highest packing factor istypically between 50% and 65% by volume even for circular-cross-sectionfibers. In contrast, as shown in FIG. 4(b), the presently inventedrectangular or flat-shaped graphene fibers can be packed into a yarnwith an essentially 100% packing factor, if so desired. The packingfactor can be adjusted to be between 20% and 100%, preferably between40% and 95%, more preferably between 60% and 90%, and most preferablybetween 70% and 85% for composite structure or filter applications. Ourresearch data have demonstrated that the flexural strength and elasticmodulus values of polymer matrix composites containing presentlyinvented graphitic fiber-based fabrics as a reinforcement phase aresignificantly higher than those of the composites containing acomparable volume fraction of conventional graphitic fibers. Thedifferences are typically between 30% and 300%.

As another example, fabrics that block entry of pathogenic agentsrequire that the yarns of highest packing factors be interwoven tightlyto prevent any gaps between one another. The thickness and shapes ofconventional fibers alone could allow significant gaps within each yarndefined by those fibers. The instant invention provides tightly packedyarns and fabrics. These features are not achievable with conventionalgraphitic fibers.

The present invention also provides a process for producing fabricscontaining graphene-based continuous or long fibers from chemicallyfunctionalized graphene sheets and, subsequently, the yarns and fabricscontaining these fibers. In certain embodiments, the process comprises:

-   -   (a) preparing a graphene dispersion having chemically        functionalized graphene sheets dispersed in a liquid medium        (e.g. water or an organic solvent), wherein the chemically        functionalized graphene sheets contain chemical functional        groups attached thereto (on graphene sheet surfaces and/or        edges) and a non-carbon element content of 0.1% to 47% by        weight;    -   (b) dispensing and depositing at least a continuous or long        filament of the graphene dispersion onto a supporting substrate,        wherein the dispensing and depositing procedure includes        mechanical shear stress-induced alignment of the chemically        functionalized graphene sheets along the filament axis        direction, and partially or completely removing the liquid        medium from the filament to form a continuous or long fiber        comprising aligned chemically functionally graphene sheets;    -   (c) using heat (typically from 0 to 200° C.), electromagnetic        waves (e.g. radio frequency waves, or microwaves), UV light,        high-energy radiation (e.g. electron beam, Gamma ray, or X-ray),        or a combination thereof to induce chemical reactions or        chemical bonding between chemical functional groups attached to        adjacent chemically functionalized graphene sheets to form the        long or continuous graphene fiber, wherein the long graphene        fiber comprises chemically functionalized graphene sheets that        are chemically bonded with one another having an inter-planar        spacing d₀₀₂ from 0.36 nm to 1.5 nm as determined by X-ray        diffraction and a non-carbon element content of 0.1% to 40% by        weight and wherein the functionalized graphene sheets are        substantially parallel to one another and parallel to the fiber        axis direction and the fiber contains no core-shell structure,        have no helically arranged graphene domains, and have a length        no less than 0.5 cm and a physical density from 1.5 to 2.25        g/cm³;    -   (d) combining at least one such continuous or long graphene        fiber with a plurality of the same type or different type(s) of        fibers to prepare continuous or long fiber yarns; and    -   (e) combining these fiber yarns and other fiber yarns (the same        or different types) into a fabric.        Preferably, multiple continuous graphene fibers of this type are        formed into yarns of a desired shape. Multiple yarns of this        type of continuous graphene fibers, alone or in combinations        with other types of fibers or yarns, are made into a fabric        using known yarn- and fabric-producing methods.

The process may further comprise a step of compressing the continuous orlong fiber (after step (b) or (c)) to increase the degree of graphenesheet orientation and physical density, and to improve the contactbetween chemically functionalized graphene sheets. This would alsofacilitate chemical interconnection between graphene sheets.

The invention also provides a process for producing a fabric containinggraphene-based long fibers from graphene sheets. In certain embodiments,the process comprises:

-   -   (a) preparing a graphene dispersion having graphene sheets        dispersed in a fluid medium (e.g., water or an organic solvent);    -   (b) dispensing and depositing at least a continuous or long        filament of the graphene dispersion onto a supporting substrate,        wherein the dispensing and depositing procedure includes        mechanical shear stress-induced alignment of the graphene sheets        along a filament axis direction, and partially or completely        removing the fluid medium from the filament to form a continuous        or long fiber comprising aligned graphene sheets;    -   (c) bringing the continuous or long fiber in contact with a        chemical functionalizing agent so as to produce a continuous or        long fiber of chemically functionalized graphene sheets having        chemical functional groups attached thereto and a non-carbon        element content (e.g. H, O, N, B, P, Cl, F, Br, I, S, etc.) of        0.1% to 47% by weight;    -   (d) using heat (typically from 0 to 200° C.), electromagnetic        waves (e.g. radio frequency waves, or microwaves), UV light,        high-energy radiation (e.g. electron beam, Gamma ray, or X-ray),        or a combination thereof to induce chemical reactions or        chemical bonding between chemical functional groups attached to        adjacent chemically functionalized graphene sheets to form said        long graphene fiber, wherein said long graphene fiber comprises        chemically functionalized graphene sheets that are chemically        bonded with one another having an inter-planar spacing d₀₀₂ from        0.36 nm to 1.5 nm as determined by X-ray diffraction and a        non-carbon element content of 0.1% to 47% by weight and wherein        said functionalized graphene sheets are substantially parallel        to one another and parallel to a fiber axis direction and said        fiber contains no core-shell structure, have no helically        arranged graphene domains, and have a length no less than 0.5 cm        and a physical density from 1.5 to 2.25 g/cm³;    -   (e) combining at least one such continuous or long graphene        fiber with a plurality of the same type or different type(s) of        fibers to prepare continuous or long fiber yarns; and    -   (f) combining these fiber yarns and other fiber yarns (the same        or different types) into a fabric.

The process may further comprise a step of compressing the continuous orlong fiber (after step (c) or (d)) to increase the degree of graphenesheet orientation and physical density, and to improve the contactbetween chemically functionalized graphene sheets.

The continuous or long graphene fiber can have a cross-section that iscircular, elliptical, rectangular, flat-shaped, or hollow depending uponthe geometry of the shaping die used. Preferred shapes of continuous orlong graphene fibers for use in the fabric are rectangular orflat-shaped. The diameter or thickness of the presently inventedgraphene fiber can be varied from nanometer scaled to millimeter-scaled;there is no restriction on the fiber diameter/thickness. This is a veryimportant feature that cannot be found in any other type of continuouscarbon fiber or graphite fiber.

For instance, the presently invented continuous or long fiber can have adiameter or thickness up to 100 μm (or greater), which cannot beobtained with conventional carbon or graphite fibers. The continuous orlong graphene fiber can have a diameter or thickness less than 10 μm oreven less than 1 μm, which is not possible with other types ofcontinuous carbon or graphite fibers having a high strength. Quitesignificantly, the continuous graphene fiber can have a diameter orthickness less than 100 nm.

The chemically functionalized graphene sheets in the continuous or longfiber may contain one or more chemical functional groups.

The process may further comprise a step of reducing the non-carboncontent to less than 20% (preferably less than 5%) by weight usingchemical, thermal, UV, or radiation-induced reduction means. Forinstance, one may optionally subject the long or continuous fiber to aheat treatment at a temperature of typically 200-700° C. to thermallyreduce the non-carbon content. However, for thermally activating therequired cross-linking or interconnecting reactions between chemicallyactive functional groups of neighboring graphene sheets, a temperaturelower than 200° C. is typically sufficient (more typically lower than150° C. and further more typically lower than 100° C. is sufficient).

In certain embodiments, the inter-plane spacing d₀₀₂ is from 0.4 nm to1.2 nm, the non-carbon element content is from 1% to 20%, or physicaldensity from 1.7 to 2.15 g/cm³.

The continuous or long fiber can have a cross-section that is circular,elliptical, rectangular, flat-shaped, or hollow. The fiber preferablyhas a length from 1 cm to 10,000 meters, a cross-section having a width(or second largest dimension) from 1 μm to 5 mm, and a thickness (orsmallest dimension) from 10 nm to 500 μm, and a width-to-thickness ratiofrom 1 to 10,000. Preferably, the long fiber has a width from 1 to 20 amand a thickness from 100 nm to 100 μm.

In certain embodiments, the long fiber has a thermal conductivity from200 to 1,600 W/mK or an electrical conductivity from 600 to 15,000 S/cm;preferably and typically having a thermal conductivity of at least 350W/mK or an electrical conductivity no less than 1,000 S/cm; furtherpreferably and typically having a thermal conductivity of at least 600W/mK or an electrical conductivity no less than 2,500 S/cm; stillfurther preferably having a thermal conductivity of at least 1,000 W/mKor an electrical conductivity no less than 5,000 S/cm; and mostpreferably having a thermal conductivity of at least 1,200 W/mK, or anelectrical conductivity no less than 8,000 S/cm.

In certain embodiments, the long fiber contains a first graphene domaincontaining bonded graphene planes parallel to one another and having afirst crystallographic c-axis, and a second graphene domain containingbonded graphene planes parallel to one another and having a secondcrystallographic c-axis wherein the first crystallographic c-axis andthe second crystallographic c-axis are inclined with respect to eachother at an angle less than 10 degrees.

The degree of graphene sheet orientation in a continuous or long fiberwas mainly measured using a well-known method based on the full width athalf maximum (FWHM) of X-ray scattering intensity as a function of theazimuthal angle. The degree of orientation may be calculated from thefollowing equation: Φ=100%×(180−FWHM)/180. The degree of orientation ofgraphene sheets in the presently invented continuous or long fibers istypically from 86% to 99% and more typically from 87% to 99%. It is ofinterest to note that the use of comma coating for graphene dispersiondeposition typically results in a continuous and long graphene fiberhaving a degree of orientation of approximately from 87% to 93%. Theslot-die coating procedure for preparing graphene fibers having aflat-shape cross-section typically leads to a degree of orientation ofapproximately from 90% to 96% and a reverse-roll coating procedure leadsto a degree of graphene sheet orientation from 93% to 99%.

In certain embodiments, the long fiber contains a combination of sp² andsp³ electronic configurations. There are graphene edge-to-edge,edge-to-graphene plane, and graphene plane-to-graphene plane bonding(covalent bonds or π-π bonds) between functionalized graphene sheets.

The invented process may further comprise a step of incorporating thelong fiber to produce a fiber yarn or bundle. In certain embodiments,the process further comprises a step of incorporating a plurality of theinvented long fibers to produce a fiber yarn or bundle.

The present invention also provides a fiber yarn (e.g. a twisted (plied)yarn, non-twist (non-plied) yarn, or braid) or bundle comprising atleast a continuous or long fiber of present invention. The yarn orbundle can also contain other type of fibers (e.g. carbon fibers) toform a hybrid yarn or bundle. The invention also provides a fiber yarnor bundle comprising a plurality of presently invented continuous orlong fibers. The invention also provides a fabric, which may be woven,braided, knit or nonwoven.

Another embodiment of the present invention is a filter that containsthe presently invented fabric as a filtering element. Such a filter isfound to have a desirable combination of filtering efficiency, filteruseful life, filter strength and structural integrity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Schematic drawing illustrating the processes for producingconventional paper, mat, film, and membrane of simply aggregatedgraphite or graphene flakes/platelets. All processes begin withintercalation and/or oxidation treatment of graphitic materials (e.g.natural graphite particles).

FIG. 2(a) A SEM image of a graphite worm sample after thermalexfoliation of graphite intercalation compounds (GICs) or graphite oxidepowders;

FIG. 2(b) An SEM image of a cross-section of a flexible graphite foil,showing many graphite flakes with orientations not parallel to theflexible graphite foil surface and also showing many defects, kinked orfolded flakes;

FIG. 2(c) SEM images of an elongated section of prior art graphenefibers produced by solution spinning and liquid coagulation, showingmany graphene sheets with orientations not parallel to the fiber axisdirection and also showing many defects, pores, kinked or foldedgraphene sheets;

FIG. 2(d) SEM images of another elongated section of prior art graphenefibers produced by solution spinning and liquid coagulation.

FIG. 3(a) A SEM image of a long graphene fiber produced from chemicallyfunctionalized GO sheets;

FIG. 3(b) A SEM image of a cross-section of a conventional graphenepaper/film prepared from discrete graphene sheets/platelets using apaper-making process (e.g. vacuum-assisted filtration). The image showsmany discrete graphene sheets being folded or interrupted (notintegrated), with orientations not parallel to the film/paper surfaceand having many defects or imperfections;

FIG. 3(c) One plausible chemical linking mechanism (only 2 GO sheets areshown as an example; a large number of GO sheets can be chemicallylinked together to form a long graphene fiber).

FIG. 4(a) Schematic diagram illustrating a process of producing multiplecontinuous graphene fibers from functionalized graphene sheets dispensedthrough multiple nozzles under the influence of a shear stress and highstrain rate;

FIG. 4(b) Two types of fiber cross-sections (circular and rectangular)forming two types of yarns with different packing factors.

FIG. 5(a) Chemical functionalization of graphene sheets, Scheme 1.

FIG. 5(b) Chemical functionalization of graphene sheets, Scheme 2.

FIG. 5(c) An example to illustrate one mechanism with which neighboringchemically functionalized graphene sheets are chemically interconnectedtogether.

FIG. 6 Tensile strength and Young's modulus of three graphene fibers:one derived from highly oriented chemically functionalized graphenesheets, one derived from highly oriented graphene oxide sheets, and aconventional coagulation-based reduced graphene oxide fiber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a fabric, and constituent yarns,containing graphene-based continuous or long fibers which comprisechemically functionalized graphene sheets that are chemically bondedinterconnected with one another having an inter-planar spacing d₀₀₂ from0.36 nm to 1.5 nm as determined by X-ray diffraction and a non-carbonelement content (e.g. H, O, N, B, P, Cl, F, Br, I, S, etc.) of 0.1% to47% by weight, wherein the functionalized graphene sheets aresubstantially parallel to one another and parallel to the fiber axisdirection and the fiber contains no core-shell structure, have nohelically arranged graphene domains, and have a length no less than 0.5cm and a physical density from 1.5 to 2.25 g/cm³. This long fiber can bean essentially “continuous fiber” wound as a spool on a roller andhaving a length up to several kilometers (e.g. 10 km). The graphenesheets are typically interconnected with one another via chemicalbonding or reactions between the chemically active functional groupsattached to respective adjacent functional groups.

The present invention also provides a process for producing a fabriccontaining graphene-based continuous or long fibers from chemicallyfunctionalized graphene sheets. In certain embodiments, the processcomprises:

-   -   (a) preparing a graphene dispersion having chemically        functionalized graphene sheets dispersed in a liquid medium        (e.g. water or an organic solvent), wherein the chemically        functionalized graphene sheets contain chemical functional        groups attached thereto (on graphene sheet surfaces and/or        edges) and a non-carbon element content of 0.1% to 47% by        weight;    -   (b) dispensing and depositing at least a continuous or long        filament of the graphene dispersion onto a supporting substrate        (e.g. using casting, slot-die coating, comma coating,        reverse-roll coating, ultrasonic spraying, or pressure        air-assisted spraying, etc.), wherein the dispensing and        depositing procedure includes applying a mechanical shear stress        to induce alignment of the chemically functionalized graphene        sheets along the filament axis direction, and partially or        completely removing the liquid medium from the filament to form        a continuous or long fiber comprising aligned chemically        functionally graphene sheets (e.g. the coating head can create a        high shear stress between the dispensed graphene dispersion and        the supporting substrate that undergoes a relative fast motion        relative to the coating head);    -   (c) using heat, electromagnetic waves (e.g. radio frequency        waves, or microwaves), UV light, high-energy radiation (e.g.        electron beam, Gamma ray, or X-ray), or a combination thereof to        induce chemical reactions or chemical bonding between chemical        functional groups attached to adjacent chemically functionalized        graphene sheets to form the long graphene fiber, wherein the        long graphene fiber comprises chemically functionalized graphene        sheets that are chemically bonded or interconnected with one        another having an inter-planar spacing d₀₀₂ from 0.36 nm to 1.5        nm as determined by X-ray diffraction and a non-carbon element        content of 0.1% to 40% by weight and wherein the functionalized        graphene sheets are substantially parallel to one another and        parallel to the fiber axis direction and the fiber contains no        core-shell structure, have no helically arranged graphene        domains, and have a length no less than 0.5 cm and a physical        density from 1.5 to 2.2 g/cm³;    -   (d) combining at least one such continuous or long graphene        fiber with a plurality of the same type or different type(s) of        fibers to prepare continuous or long fiber yarns; and    -   (e) combining these fiber yarns and other fiber yarns (the same        or different types) into a fabric.

It is important to note that multiple filaments can be producedconcurrently if we dispense and form multiple continuous filaments offunctionalized graphene sheets onto a supporting substrate at the sametime. There is no limitation as to how many filaments can be generatedat the same time. Hundreds, thousands, or tens of thousands of filamentscan be made and combined into a continuous yarn when or after thesefilaments are made.

Step (a) includes dispersing chemically functionalized graphene sheetsin a liquid medium, such as water or organic solvent. The production ofgraphene sheets is well-known in the art. Some details about how toprepare graphene dispersion in step (a) of the invented process arepresented below.

As an example, a graphite intercalation compound (GIC) or graphite oxidemay be obtained by immersing powders or filaments of a startinggraphitic material in an intercalating/oxidizing liquid medium (e.g. amixture of sulfuric acid, nitric acid, and potassium permanganate) in areaction vessel. The starting graphitic material may be selected fromnatural graphite, artificial graphite, mesophase carbon, mesophasepitch, mesocarbon microbead, soft carbon, hard carbon, coke, carbonfiber, carbon nanofiber, carbon nanotube, or a combination thereof.

When the starting graphite powders or filaments are mixed in theintercalating/oxidizing liquid medium, the resulting slurry is aheterogeneous suspension and appears dark and opaque. When the oxidationof graphite proceeds at a reaction temperature for a sufficient lengthof time (4-120 hours at room temperature, 20-25° C.), the reacting masscan eventually become a suspension that appears slightly green andyellowish, but remain opaque. If the degree of oxidation is sufficientlyhigh (e.g. having an oxygen content between 20% and 50% by weight,preferably between 30% and 50%) and all the original graphene planes arefully oxidized, exfoliated and separated to the extent that eachoxidized graphene plane (now a graphene oxide sheet or molecule) issurrounded by the molecules of the liquid medium, one obtains a GO gel.

The aforementioned features are further described and explained indetail as follows: As illustrated in FIG. 1, a graphite particle (e.g.100) is typically composed of multiple graphite crystallites or grains.A graphite crystallite is made up of layer planes of hexagonal networksof carbon atoms. These layer planes of hexagonally arranged carbon atomsare substantially flat and are oriented or ordered so as to besubstantially parallel and equidistant to one another in a particularcrystallite. These layers of hexagonal-structured carbon atoms, commonlyreferred to as graphene layers or basal planes, are weakly bondedtogether in their thickness direction (crystallographic c-axisdirection) by weak van der Waals forces and groups of these graphenelayers are arranged in crystallites. The graphite crystallite structureis usually characterized in terms of two axes or directions: the c-axisdirection and the a-axis (or b-axis) direction. The c-axis is thedirection perpendicular to the basal planes. The a- or b-axes are thedirections parallel to the basal planes (perpendicular to the c-axisdirection).

A highly ordered graphite particle can consist of crystallites of aconsiderable size, having a length of L_(a) along the crystallographica-axis direction, a width of L_(b) along the crystallographic b-axisdirection, and a thickness L_(c) along the crystallographic c-axisdirection. The constituent graphene planes of a crystallite are highlyaligned or oriented with respect to each other and, hence, theseanisotropic structures give rise to many properties that are highlydirectional. For instance, the thermal and electrical conductivity of acrystallite are of great magnitude along the plane directions (a- orb-axis directions), but relatively low in the perpendicular direction(c-axis). As illustrated in the upper-left portion of FIG. 1, differentcrystallites in a graphite particle are typically oriented in differentdirections and, hence, a particular property of a multi-crystallitegraphite particle is the directional average value of all theconstituent crystallites.

Due to the weak van der Waals forces holding the parallel graphenelayers, natural graphite can be treated so that the spacing between thegraphene layers can be appreciably opened up so as to provide a markedexpansion in the c-axis direction, and thus form an expanded graphitestructure in which the laminar character of the carbon layers issubstantially retained. The process for manufacturing flexible graphiteis well-known in the art. In general, flakes of natural graphite (e.g.100 in FIG. 1) are intercalated in an acid solution to produce graphiteintercalation compounds (GICs, 102). The GICs are washed, dried, andthen exfoliated by exposure to a high temperature for a short period oftime. This causes the flakes to expand or exfoliate in the c-axisdirection of the graphite up to 80-300 times of their originaldimensions. The exfoliated graphite flakes are vermiform in appearanceand, hence, are commonly referred to as worms 104. These worms ofgraphite flakes which have been greatly expanded can be formed withoutthe use of a binder into cohesive or integrated sheets of expandedgraphite, e.g. webs, papers, strips, tapes, foils, mats or the like(typically referred to as “flexible graphite” 106) having a typicaldensity of about 0.04-2.0 g/cm³ for most applications.

In one prior art process, the exfoliated graphite (or mass of graphiteworms) is re-compressed by using a calendaring or roll-pressingtechnique to obtain flexible graphite foils (106 in FIG. 1), which aretypically 100-300 μm thick.

Largely due to the presence of defects, commercially available flexiblegraphite foils normally have an in-plane electrical conductivity of1,000-3,000 S/cm, through-plane (thickness-direction or Z-direction)electrical conductivity of 15-30 S/cm, in-plane thermal conductivity of140-300 W/mK, and through-plane thermal conductivity of approximately10-30 W/mK. These defects are also responsible for the low mechanicalstrength (e.g. defects are potential stress concentration sites wherecracks are preferentially initiated). These properties are inadequatefor many thermal management applications and the present invention ismade to address these issues. In another prior art process, theexfoliated graphite worm may be impregnated with a resin and thencompressed and cured to form a flexible graphite composite, which isnormally of low strength as well. In addition, upon resin impregnation,the electrical and thermal conductivity of the graphite worms could bereduced by two orders of magnitude.

Alternatively, the exfoliated graphite may be subjected tohigh-intensity mechanical shearing/separation treatments using ahigh-intensity air jet mill, high-intensity ball mill, or ultrasonicdevice to produce separated nano graphene platelets (NGPs) with all thegraphene platelets thinner than 100 nm, mostly thinner than 10 nm, and,in many cases, being single-layer graphene (also illustrated as 112 inFIG. 1). An NGP is composed of a graphene sheet or a plurality ofgraphene sheets with each sheet being a two-dimensional, hexagonalstructure of carbon atoms.

Further alternatively, with a low-intensity shearing, graphite wormstend to be separated into the so-called expanded graphite flakes (108 inFIG. 1) having a thickness >100 nm. These flakes can be formed intographite paper or mat 106 using a paper- or mat-making process. Thisexpanded graphite paper or mat 106 is just a simple aggregate or stackof discrete flakes having defects, interruptions, and mis-orientationsbetween these discrete flakes.

For the purpose of defining the geometry and orientation of an NGP, theNGP is described as having a length (the largest dimension), a width(the second largest dimension), and a thickness. The thickness is thesmallest dimension, which is no greater than 100 nm, preferably smallerthan 10 nm and most preferably 0.34 nm-1.7 nm in the presentapplication. When the platelet is approximately circular in shape, thelength and width are referred to as diameter. In the presently definedNGPs, both the length and width can be smaller than 1 μm, but can belarger than 200 μm.

A mass of multiple NGPs (including discrete sheets/platelets ofsingle-layer and/or few-layer graphene or graphene oxide) may be readilydispersed in water or a solvent and then made into a graphene paper (114in FIG. 1) using a paper-making process. Many discrete graphene sheetsare folded or interrupted (not integrated), most of plateletorientations being not parallel to the paper surface. The existence ofmany defects or imperfections leads to poor electrical and thermalconductivity in both the in-plane and the through-plane (thickness-)directions.

Fluorinated graphene or graphene fluoride is herein used as an exampleof the halogenated graphene material group. There are two differentapproaches that have been followed to produce fluorinated graphene: (1)fluorination of pre-synthesized graphene: This approach entails treatinggraphene prepared by mechanical exfoliation or by CVD growth withfluorinating agent such as XeF₂, or F-based plasmas; (2) Exfoliation ofmultilayered graphite fluorides: Both mechanical exfoliation and liquidphase exfoliation of graphite fluoride can be readily accomplished [F.Karlicky, et al. “Halogenated Graphenes: Rapidly Growing Family ofGraphene Derivatives” ACS Nano, 2013, 7 (8), pp 6434-6464].

Interaction of F₂ with graphite at high temperature leads to covalentgraphite fluorides (CF)_(n) or (C₂F)_(n), while at low temperaturesgraphite intercalation compounds (GIC) C_(x)F (2≤x≤24) form. In (CF)_(n)carbon atoms are sp3-hybridized and thus the fluorocarbon layers arecorrugated consisting of trans-linked cyclohexane chairs. In (C₂F)_(n)only half of the C atoms are fluorinated and every pair of the adjacentcarbon sheets are linked together by covalent C—C bonds. Systematicstudies on the fluorination reaction showed that the resulting F/C ratiois largely dependent on the fluorination temperature, the partialpressure of the fluorine in the fluorinating gas, and physicalcharacteristics of the graphite precursor, including the degree ofgraphitization, particle size, and specific surface area. In addition tofluorine (F₂), other fluorinating agents may be used, although most ofthe available literature involves fluorination with F₂ gas, sometimes inpresence of fluorides.

For exfoliating a layered precursor material to the state of individualsingle graphene layers or few-layers, it is necessary to overcome theattractive forces between adjacent layers and to further stabilize thelayers. This may be achieved by either covalent modification of thegraphene surface by functional groups or by non-covalent modificationusing specific solvents, surfactants, polymers, or donor-acceptoraromatic molecules. The process of liquid phase exfoliation includesultra-sonic treatment of a graphite fluoride in a liquid medium toproduce graphene fluoride sheets dispersed in the liquid medium. Theresulting dispersion can be directly made into a sheet of paper or aroll of paper.

The nitrogenation of graphene can be conducted by exposing a graphenematerial, such as graphene oxide, to ammonia at high temperatures(200-400° C.). Nitrogenated graphene could also be formed at lowertemperatures by a hydrothermal method; e.g. by sealing GO and ammonia inan autoclave and then increased the temperature to 150-250° C. Othermethods to synthesize nitrogen doped graphene include nitrogen plasmatreatment on graphene, arc-discharge between graphite electrodes in thepresence of ammonia, ammonolysis of graphene oxide under CVD conditions,and hydrothermal treatment of graphene oxide and urea at differenttemperatures.

For the purpose of defining the claims of the instant application, NGPsor graphene materials include discrete sheets/platelets of single-layerand multi-layer (typically less than 10 layers, the few-layer graphene)pristine graphene, graphene oxide, reduced graphene oxide (RGO),graphene fluoride, graphene chloride, graphene bromide, graphene iodide,hydrogenated graphene, nitrogenated graphene, chemically functionalizedgraphene, doped graphene (e.g. doped by B or N). Pristine graphene hasessentially 0% oxygen. RGO typically has an oxygen content of 0.001%-5%by weight. Graphene oxide (including RGO) can have 0.001%-50% by weightof oxygen. Other than pristine graphene, all the graphene materials have0.001%-50% by weight of non-carbon elements (e.g. O, H, N, B, F, Cl, Br,I, etc.). These materials are herein referred to as non-pristinegraphene materials. The presently invented graphene fiber can containpristine or non-pristine graphene and the invented method allows forthis flexibility.

Several methods have been developed to chemically functionalize graphenesheets (including pristine graphene, graphene oxide, and reducedgraphene oxide or rGO). The reader may consult this review article:Vasilios Georgakilas, et al. “Functionalization of Graphene: Covalentand Non-Covalent Approaches, Derivatives and Applications,” Chem. Rev.,2012, 112 (11), pp 6156-6214; DOI: 10.1021/cr3000412.

Pristine graphene is one of the most chemically inert materials becausehigh energy barriers need to be overcome due to the rigid planarstructure and remarkable interlayer conjugation. By diazonium chemistryand photochemistry, various functional groups have been grafted ontographene. For the diazonium chemistry, stirring-assisted solutionreaction may be tedious. For the photochemistry, either a focused laserspot may be used to generate a sufficiently high intensity, resulting ina localized functionalization of graphene sheets. A heat-initiatedchemical reaction can be used to functionalize pristine grapheneprepared by chemical vapor deposition (CVD) or liquid phase exfoliation.

The organic covalent functionalization reactions of graphene include twogeneral routes: (a) the formation of covalent bonds between freeradicals or dienophiles and C═C bonds of pristine graphene and (b) theformation of covalent bonds between organic functional groups and theoxygen groups of GO. The most attractive organic species for thereaction with sp2 carbons of graphene are organic free radicals anddienophiles. Usually both are intermediate reactive components that areproduced under certain conditions in the presence of graphene.

Upon heating of a diazonium salt, a highly reactive free radical isproduced, which attacks the sp2 carbon atoms of graphene, therebyforming a covalent bond. This reaction can be used to decorate graphenewith nitrophenyls. The strong covalent binding of the nitrobenzyl groupon graphene may be detected by X-ray photoelectron spectroscopy (XPS).The N1s XPS spectrum of the functionalized graphene normally exhibitstwo peaks at 406 and 400 eV that correspond to the nitrogen of NO₂ andthe partially reduced nitrogen of the product, respectively. Thereactions with diazonium salts have been applied to thefunctionalization of chemically or thermally converted graphene, singlegraphene sheets obtained by micromechanical cleavage from bulk graphite,and epitaxial graphene.

Hydroxylated aryl groups can be grafted covalently on graphene by thediazonium addition reaction. The ratio between carbon atoms with sp2 andsp3 hybridization in the graphitic lattice is an indication of thedegree of oxidation or a covalent functionalization reaction. This ratiomay be estimated using Raman spectroscopy as the ID/IG ratio, where IDand IG are the intensities of the peaks at ˜1350 and 1580 cm⁻¹, whichcorrespond to the number of sp3 and sp2 C atoms, respectively. Grapheneis often defined as a pristine two-dimensional sp2 hybridized carbonsheet; as such the coexistence of sp3 carbons in the lattice areinherently classified as defects, where these defects can be on thebasal edges or inside defects in the plane. For the modificationdescribed above, the ID/IG ratio is increased from 1.7 to ˜2 afterfunctionalization by diazonium addition.

An alternative free radical addition method includes the reaction ofbenzoyl peroxide with graphene sheets. Graphene sheets may be depositedon a silicon substrate and immersed in a benzoyl peroxide/toluenesolution. The reaction is then initiated photochemically by focusing anAr-ion laser beam onto the graphene sheets in the solution. Theattachment of the phenyl groups is directly indicated by the appearanceof a strong D band at 1343 cm⁻¹. The appearance of this D band is due tothe formation of sp3 carbon atoms in the basal plane of graphene bycovalent attachment of phenyl groups.

A type of metalized graphene, potassium graphene, may be used in thereaction with 1-iododecane to produce dodecylated graphene (Scheme 1,FIG. 5(A)). The FT-IR spectra can be used to confirm presence of C—Hstretching bands at 2800-3000 cm⁻¹ associated with the dodecyl groups.TGA may indicate a weight loss of 15%, which corresponds to about onedodecyl group per 78 graphite carbon atoms. The resulting dodecylatedgraphene is soluble in chloroform, benzene, and 1,2,4-trichlorobenzene.Additionally, its solubility in water can be achieved by the reaction ofpotassium graphene with 5-bromovaleric acid and subsequent reaction withamine-terminated PEG (see Scheme 1).

Top-down approaches may be used to prepare chemically-functionalizedgraphene with an objective to make them dispersible in a selected liquidmedium. For instance, graphene oxide (GO) nanosheets having ample oxygenfunctionalities in the basal plane and along the edges may beselectively targeted for the chemical functionalization. In a firstapproach, for instance, octadecylamine (ODA) can be covalently graftedon the edges of reduced graphene oxide (rGO) via amide linkage and thiscan be confirmed by FTIR and XPS analyses. In a second approach, oxygenfunctionalities in the basal plane of GO can be selected to tether theoctadecylamine via covalent, charge-induced electrostatic and hydrogenlinkages between the amino group of ODA and epoxy, carboxylic andhydroxyl functionalities of GO, respectively. The chemical andstructural features of products may be examined by FTIR, ¹³C NMR, XPS,XRD and HRTEM. In a third approach, rGO can be covalently functionalizedwith imidazolium ionic liquids having bis(salicylato)borate, oleate andhexafluorophosphate anions. Chemical functionalized graphene may also beobtained by the reaction of the residual epoxide and carboxyl functionalgroups on the hydrazine-reduced graphene sheets with hydroquinone.

A simple method often used for the functionalization of graphene isbased on reactions of the carboxyl groups, present in GO and located atthe edges of graphene sheets, with various amines or alcohols. Reactionsof the graphene carboxyl groups with amines, leading to the formation ofamides, were performed via various more reactive intermediates (seeScheme 2, FIG. 5(B)). As one example, to prepare graphene soluble innon-polar solvents, the acid-treated graphene is reacted with an excessof thionyl chloride (SOCl₂) and subsequently heated with dodecylamine.Defected graphene requires a harsher acid treatment over longer periodsto enable its further functionalization. The functionalization may beconfirmed by a shift in the C═O stretching band to 1650 cm⁻¹ due to theamide band and an appearance of C—H and N—H stretching bands at 2800 and3300 cm⁻¹ as observed by FT-IR spectroscopy. Dodecylamide-functionalizedgraphene is dispersible in dichlormethane, carbon tetrachloride (CCl₄)and tetrahydrofuran (THF). A similar approach via an acyl chlorideintermediate may also be used for the modification of graphite oxidewith octadecylamine (ODA).

In yet another approach, graphene oxide sheets are immersed in asolution of 10,12-pentacosadiyn-1-ol [PCO, CH₃(CH₂)₁₁C≡C—C≡C(CH₂)₈CH₂OH]to form a graphene dispersion. The dispersion is then coated on a PETsubstrate under a high shear stress and high shear rate condition (shearrate from 0.1 to 10⁵ sec⁻¹, preferably from 10² to 10⁴ sec⁻¹) to form afilament comprising highly oriented GO sheets lightly coated with PCO.As illustrated in Scheme 3, FIG. 5(C), the filament, after drying, maybe exposed to UV light to provide a fiber of PCO-GO sheets in which thediacetylene groups of PCO have reacted by 1,4-addition polymerization.Subsequently, the fiber may be immersed in hydroiodic acid (HI) toreduce the PCO-GO sheets into graphene-PCO sheets. Then, the fiber ofgraphene-PCO sheets is immersed successively into 1-pyrenebutyric acidN-hydroxysuccinimide ester (PSE) and 1-aminopyrene (AP) solutions,thereby providing a fiber of interconnected graphene sheet in which thePSE and AP have bonded through π-π interactions with neighboringgraphene sheets and reacted to provide PSE-AP covalent bonds. The ratioof π-π interactions through PSE-AP derived bonding and covalent bondingresulting from PCO can be optimized by adjusting the immersion times inthe respective solutions.

The above discussion indicates that chemical functionalization plays atleast two roles in the instant invention. One is to make a graphenematerial (e.g. pristine graphene, GO, RGO, graphene fluoride, etc.)dispersible in a desired liquid medium so that we can produce a graphenedispersion for subsequent production of long or continuous graphenefibers. A second role is to create bridging functional groups thatenable chemical reactions, merging, and/or cross-linking betweenfunctionalized graphene sheets to produce graphene fibers consisting ofessentially interconnected graphene sheets to impart high strength, highelasticity, high electric conductivity and high thermal conductivity.

Step (b) includes dispensing and depositing at least a continuous orlong filament of the graphene dispersion onto a supporting substrate.This can be accomplished by using casting, slot-die coating, commacoating, reverse-roll coating, ultrasonic spraying, or pressureair-assisted spraying, etc.). In these operations, the dispensing anddepositing procedure preferably includes using mechanical shear stressto align or orient the chemically functionalized graphene sheets alongthe filament axis direction. In certain embodiments, the coating headcan be operated to create a high shear stress and high strain ratebetween the dispensed graphene dispersion and the supporting substratethat undergoes a relative motion relative to the coating head.

This mechanical stress/strain condition enables all the constituentgraphene sheets or graphene domains to be aligned along the graphenefiber axis direction and be substantially parallel to one another. Moresignificantly, the graphene sheets are closely packed to facilitatechemical reactions or cross-linking (interconnection) between graphenesheets. In other words, not only the graphene planes in a particulardomain are parallel to one another, they are also parallel to thegraphene planes in the adjacent domain. The crystallographic c-axes ofthese two sets of graphene planes are pointing along substantiallyidentical directions. As such, the domains do not follow a helical ortwisting pattern. Thus, the continuous graphene fiber contains a firstgraphene domain containing bonded graphene sheets parallel to oneanother and having a first crystallographic c-axis, and a secondgraphene domain containing bonded graphene sheets parallel to oneanother and having a second crystallographic c-axis wherein the firstcrystallographic c-axis and the second crystallographic c-axis areinclined with respect to each other at an angle less than 10 degrees(mostly less than 5% and even more often less than 1 degree).

As schematically illustrated in FIG. 4(a), multiple dispensing devicesor one dispensing device with multiple nozzles may be used to dispensemultiple filaments of graphene sheets onto a moving substrate in acontinuous manner. A feeder roller provides a solid substrate (e.g.plastic film) that moves from the left side to the right side of FIG.4(a) and is collected on a take-up roller. A drying/heating zone may beimplemented to remove most of the liquid component (e.g. water ororganic solvent) from the filaments prior to being collected on thewinding roller. Multiple filaments may be laid onto the substrateconcurrently.

Step (c) entails using heat, electromagnetic waves (e.g. radio frequencywaves or microwaves), UV light, high-energy radiation (e.g. electronbeam, Gamma ray, or X-ray), or a combination thereof to induce chemicalreactions or chemical bonding between chemical functional groupsattached to adjacent chemically functionalized graphene sheets to formthe long graphene fiber. The chemical functional groups and the chemicalreaction conditions (including graphene sheet orientation,close-packing, etc.) enable the formation of a long graphene fibercomprising chemically functionalized graphene sheets that are chemicallybonded with one another having an inter-planar spacing d₀₀₂ from 0.36 nmto 1.5 nm as determined by X-ray diffraction and a non-carbon elementcontent of 0.1% to 40% by weight. The functionalized graphene sheets aresubstantially parallel to one another and parallel to the fiber axisdirection and the fiber contains no core-shell structure, have nohelically arranged graphene domains, and have a length no less than 0.5cm and a physical density from 1.5 to 2.25 g/cm³.

In certain embodiments, chemical functionalization of graphene sheets isallowed to occur after the graphene fiber is formed. Thus, the inventionalso provides a process for producing a graphene-based continuous orlong fiber (or multiple fibers of this type, yarns, and fabric) frominitially un-functionalized graphene sheets. In certain embodiments, theprocess comprises:

-   -   (a) preparing a graphene dispersion having graphene sheets        dispersed in a fluid medium (e.g., water or an organic solvent);    -   (b) dispensing and depositing at least a continuous or long        filament of the graphene dispersion onto a supporting substrate,        wherein the dispensing and depositing procedure includes        mechanical shear stress-induced alignment of the graphene sheets        along a filament axis direction, and partially or completely        removing the fluid medium from the filament to form a continuous        or long fiber comprising aligned graphene sheets;    -   (c) bringing the continuous or long fiber(s) in contact with a        chemical functionalizing agent so as to produce a continuous or        long fiber of chemically functionalized graphene sheets having        chemical functional groups attached thereto and a non-carbon        element content (e.g. H, O, N, B, P, Cl, F, Br, I, S, etc.) of        0.1% to 47% by weight;    -   (d) using heat (typically from 0 to 200° C.), electromagnetic        waves (e.g. radio frequency waves, or microwaves), UV light,        high-energy radiation (e.g. electron beam, Gamma ray, or X-ray),        or a combination thereof to induce chemical reactions or        chemical bonding between chemical functional groups attached to        adjacent chemically functionalized graphene sheets to form said        long graphene fiber, wherein said long graphene fiber comprises        chemically functionalized graphene sheets that are chemically        bonded with one another having an inter-planar spacing d₀₀₂ from        0.36 nm to 1.5 nm as determined by X-ray diffraction and a        non-carbon element content of 0.1% to 47% by weight and wherein        said functionalized graphene sheets are substantially parallel        to one another and parallel to a fiber axis direction and said        fiber contains no core-shell structure, have no helically        arranged graphene domains, and have a length no less than 0.5 cm        and a physical density from 1.5 to 2.2 g/cm³;    -   (e) combining at least one such continuous or long graphene        fiber with a plurality of the same type or different type(s) of        fibers to prepare continuous or long fiber yarns; and    -   (f) combining these fiber yarns and other fiber yarns (the same        or different types) into a fabric.

In this process, graphene sheets are not functionalized initially. Theyare functionalized after the graphene sheets are made into a fiber.

A wide variety of chemical functional groups can be chemically attachedto the edges and/or planes of graphene sheets to enable interconnectionbetween graphene sheets. The chemically functionalized graphene sheetsin the long fiber may contain a chemical functional group selected fromthe group consisting of alkyl or aryl silane, alkyl or aralkyl group,hydroxyl group, carboxyl group, carboxylic group, amine group, sulfonategroup (—SO₃H), aldehydic group, quinoidal, fluorocarbon, derivativesthereof, and combinations thereof.

The chemically functionalized graphene sheets may contain a chemicalfunctional group selected from a derivative of an azide compoundselected from the group consisting of 2-azidoethanol,3-azidopropan-1-amine, 4-(2-azidoethoxy)-4-oxobutanoic acid,2-azidoethyl-2-bromo-2-methylpropanoate, chlorocarbonate,azidocarbonate, dichlorocarbene, carbene, aryne, nitrene,(R-)-oxycarbonyl nitrenes, where R=any one of the following groups,

and combinations thereof.

The chemically functionalized graphene sheets may contain a chemicalfunctional group selected from an oxygenated group consisting ofhydroxyl, peroxide, ether, keto, aldehyde, and combinations thereof.

The chemically functionalized graphene sheets may contain a chemicalfunctional group selected from the group consisting of —SO₃H, —COOH,—NH₂, —OH, —R′CHOH, —CHO, —CN, —COCl, halide, —COSH, —SH, —COOR′, —SR′,—SiR′₃, —Si(—O—SiR′₂—)OR′, —R″, Li, AlR′₂, Hg—X, TlZ₂ and Mg—X; whereiny is an integer equal to or less than 3, R′ is hydrogen, alkyl, aryl,cycloalkyl, or aralkyl, cycloaryl, or poly(alkylether), R″ isfluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl or cycloaryl, Xis halide, and Z is carboxylate or trifluoroacetate, derivativesthereof, and combinations thereof.

The chemically functionalized graphene sheets may contain a chemicalfunctional group selected from the group consisting of amidoamines,polyamides, aliphatic amines, modified aliphatic amines, cycloaliphaticamines, aromatic amines, anhydrides, ketimines, diethylenetriamine(DETA), triethylene-tetramine (TETA), tetraethylene-pentamine (TEPA),polyethylene polyamine, polyamine epoxy adduct, phenolic hardener,non-brominated curing agent, non-amine curatives, derivatives thereof,and combinations thereof.

The chemically functionalized graphene sheets may contain a chemicalfunctional group selected from OY, NHY, O═C—OY, P═C—NR′Y, O═C—SY, O═C—Y,—CR′1-OY, NY or C′Y, a derivative thereof, or a combination thereof, andY is a functional group of a protein, a peptide, an amino acid, anenzyme, an antibody, a nucleotide, an oligonucleotide, an antigen, or anenzyme substrate, enzyme inhibitor or the transition state analog of anenzyme substrate or is selected from R′—OH, R′—NR′₂, R′SH, R′CHO, R′CN,R′X, R′N⁺(R′)₃X⁻, R′SiR′₃, R′Si(—OR′—)_(y)R′_(3-y), R′Si(—O—SiR′₂—)OR′,R′—R″, R′—N—CO, (C₂H₄O—)_(w)H, (—C₃H₆O—)_(w)H, (—C₂H₄O)_(w)—R′,(C₃H₆O)_(w)—R′, R′, and w is an integer greater than one and less than200.

The chemically functionalized graphene sheets may contain a chemicalfunctional group selected from the group consisting of10,12-pentacosadiyn-1-ol, 1-pyrenebutyric acid N-hydroxysuccinimideester, 1-aminopyrene, derivatives thereof, and combinations thereof.

The process may further comprise a step (d) of compressing the graphenefibers after formation to increase the physical density of the fiber andfurther align the constituent graphene sheets.

The process may further comprise a step of reducing the non-carboncontent to less than 20% (preferably less than 5%) by weight usingchemical, thermal, UV, or radiation-induced reduction means. Forinstance, one may optionally subject the long or continuous fiber to aheat treatment at a temperature typically 200-700° C. to thermallyreduce the non-carbon content.

The functionalized graphene sheet-derived graphene fibers and relatedprocesses have the following characteristics and advantages:

-   -   (1) The presently invented graphene-based fiber is an integrated        graphene phase composed of chemically interconnected graphene        sheets that are essentially oriented parallel to one another.        The graphene sheets are also closely packed to exhibit a high        physical density. This conclusion was drawn after an extensive        investigation using a combination of SEM, TEM, selected area        diffraction (with a TEM), X-ray diffraction, atomic force        microscopy (AFM), Raman spectroscopy, and FTIR.    -   (2) The yarn-like graphene fibers prepared by the prior art        processes (e.g. spinning-coagulation) are a simple, un-bonded        aggregate/stack of multiple discrete platelets or sheets of        graphene, GO, or RGO that are just mechanically fastened        together. In contrast, the present graphene fiber of the present        invention is a fully integrated monolith containing essentially        no discrete sheets or platelets. All the graphene sheets are        chemically interconnected.    -   (3) With these conventional processes, the constituent graphene        sheets of the resulting yarn-like fibers remain as discrete        flakes/sheets/platelets that can be easily discerned or clearly        observed. In a cross-sectional view under a SEM (e.g. FIG.        2(c)), these discrete sheets are relatively random in        orientation and have many pores between these discrete sheets.    -   (4) In contrast, the preparation of the presently invented        graphene fiber structure involves chemically functionalizing        graphene sheets so that they that possess highly reactive        functional groups (e.g. —OH, —NH₂, and —COOH) at the edge and on        graphene planes. When being heated or exposed to UV or        high-energy radiation, these highly reactive functional groups        from adjacent graphene sheets react and chemically join with one        another in lateral directions along graphene planes (in an        edge-to-edge manner) and between graphene planes.

Not wishing to be bound by the theory, we offer another plausiblechemical linking mechanism as illustrated in FIG. 3(d), where only 2aligned functionalized graphene sheets are shown as an example, althougha large number of graphene sheets can be chemically linked together toform a graphene fiber. Further, chemical linking could also occurface-to-face or face-to-edge, not just edge-to-edge. These linking andmerging reactions proceed in such a manner that the graphene sheets canbe chemically merged, linked, and integrated into one single entity ormonolith.

Due to these unique chemical compositions (including non-carboncontent), morphology, crystal structure (including inter-graphenespacing), and microstructural features (e.g. defects, chemical bondingand no gap between graphene sheets, nearly perfectly aligned graphenesheets, and no interruptions in graphene planes), the graphene-basedlong or continuous fiber has a unique combination of outstanding thermalconductivity, electrical conductivity, tensile strength, and Young'smodulus. No prior art continuous fiber of any material type even comesclose to these combined properties. Again, specifically and mostsignificantly, these chemically functionalized graphene sheets arecapable of chemically bonding, linking, or merging with one another andbecoming integrated into highly parallel and interconnected graphenesheets (e.g. FIG. 3(a)).

It may be noted that the degree of graphene sheet orientation in acontinuous or long fiber can be measured using a well-known method basedon the full width at half maximum (FWHM) of X-ray scattering intensityas a function of the azimuthal angle. The degree of orientation may becalculated from the following equation: Φ=100%×(180−FWHM)/180. It is ofinterest to note that the use of comma coating for graphene dispersiondeposition typically results in a continuous and long graphene fiberhaving a degree of orientation of approximately from 87% to 93%. Theslot-die coating procedure for preparing graphene fibers having aflat-shape cross-section typically leads to a degree of orientation ofapproximately from 90% to 96% and a reverse-roll coating procedure leadsto a degree of graphene sheet orientation from 93% to 99%.

Due to these compositional and structural features, the produced long orcontinuous fiber has a thermal conductivity from 200 to 1,600 W/mK, oran electrical conductivity from 600 to 15,000 S/cm; more preferably andtypically having a thermal conductivity of at least 350 W/mK or anelectrical conductivity no less than 1,000 S/cm; further more preferablyand typically having a thermal conductivity of at least 600 W/mK or anelectrical conductivity no less than 2,500 S/cm; still furtherpreferably and typically having a thermal conductivity of at least 1,000W/mK or an electrical conductivity no less than 5,000 S/cm; and mostpreferably having a thermal conductivity of at least 1,200 W/mK, or anelectrical conductivity no less than 8,000 S/cm. The long or continuousfiber typically and preferably has a Young's modulus from 20 GPa to 300GPa (more typically from 30 GPa to 150 GPa), or a tensile strength from1.0 GPa to 5.0 GPa (more typically from 1.2 GPa to 3.0 GPa).

The following examples are used to illustrate some specific detailsabout the best modes of practicing the instant invention and should notbe construed as limiting the scope of the invention.

Example 1: Preparation of Single-Layer Graphene Sheets from MesocarbonMicrobeads MCMBs

Mesocarbon microbeads (MCMBs) were supplied from China Steel ChemicalCo., Kaohsiung, Taiwan. This material has a density of about 2.24 g/cm³with a median particle size of about 16 μm. MCMB (10 grams) wereintercalated with an acid solution (sulfuric acid, nitric acid, andpotassium permanganate at a ratio of 4:1:0.05) for 48-96 hours. Uponcompletion of the reaction, the mixture was poured into deionized waterand filtered. The intercalated MCMBs were repeatedly washed in a 5%solution of HCl to remove most of the sulfate ions. The sample was thenwashed repeatedly with deionized water until the pH of the filtrate wasno less than 4.5. The slurry was then subjected ultrasonication for10-100 minutes to produce GO suspensions. TEM and atomic forcemicroscopic studies indicate that most of the GO sheets weresingle-layer graphene when the oxidation treatment exceeded 72 hours,and 2- or 3-layer graphene when the oxidation time was from 48 to 72hours.

The GO sheets contain oxygen proportion of approximately 35%-47% byweight for oxidation treatment times of 48-96 hours. GO sheets weresuspended in water. The GO suspension was formed into small filaments ona glass surface.

Example 2: Preparation of Pristine Graphene Sheets 0% Oxygen

Recognizing the possibility of the high defect population in GO sheetsacting to reduce the conductivity of individual graphene plane, wedecided to study if the use of pristine graphene sheets (non-oxidizedand oxygen-free, non-halogenated and halogen-free, etc.) can lead to agraphene fiber having a higher thermal conductivity. Pristine graphenesheets were produced by using the direct ultrasonication or liquid-phaseproduction process.

In a typical procedure, five grams of graphite flakes, ground toapproximately 20 μm or less in sizes, were dispersed in 1,000 mL ofdeionized water (containing 0.1% by weight of a dispersing agent, Zonyl®FSO from DuPont) to obtain a suspension. An ultrasonic energy level of85 W (Branson 5450 Ultrasonicator) was used for exfoliation, separation,and size reduction of graphene sheets for a period of 15 minutes to 2hours. The resulting graphene sheets are pristine graphene that havenever been oxidized and are oxygen-free and relatively defect-free.There are no other non-carbon elements.

The pristine graphene sheets were immersed into a 10 mM acetone solutionof BPO for 30 min and were then taken out drying naturally in air. Theheat-initiated chemical reaction to functionalize graphene sheets wasconducted at 80° C. in a high-pressure stainless steel container filledwith pure nitrogen. Subsequently, the samples were rinsed thoroughly inacetone to remove BPO residues for subsequent Raman characterization. Asthe reaction time increased, the characteristic disorder-induced D bandaround 1330 cm⁻¹ emerged and gradually became the most prominent featureof the Raman spectra. The D-band is originated from the A_(1g) modebreathing vibrations of six-membered sp² carbon rings, and becomes Ramanactive after neighboring sp² carbon atoms are converted to sp³hybridization. In addition, the double resonance 2D band around 2670cm⁻¹ became significantly weakened, while the G band around 1580 cm⁻¹was broadened due to the presence of a defect-induced D′ shoulder peakat 1620 cm⁻¹. These observations suggest that covalent C—C bonds wereformed and thus a degree of structural disorder was generated by thetransformation from sp² to sp³ configuration due to reaction with BPO.

The functionalized graphene sheets were re-dispersed in water to producea graphene dispersion. The dispersion was then made into multiplefilaments.

Example 3: Preparation of Graphene Oxide (GO) Suspension from NaturalGraphite

Graphite oxide was prepared by oxidation of graphite flakes with anoxidizer liquid consisting of sulfuric acid, sodium nitrate, andpotassium permanganate at a ratio of 4:1:0.05 at 30° C. When naturalgraphite flakes (particle sizes of 14 μm) were immersed and dispersed inthe oxidizer mixture liquid for 48 hours, the suspension or slurryappears and remains optically opaque and dark. After 48 hours, thereacting mass was rinsed with water 3 times to adjust the pH value to atleast 3.0. A final amount of water was then added to prepare a series ofGO-water suspensions. We observed that GO sheets form a liquid crystalphase when GO sheets occupy a weight fraction >3% and typically from 5%to 15%.

By dispensing and coating the GO suspension to form multiple filamentson a polyethylene terephthalate (PET) film in a slurry coater andremoving the liquid medium from the coated filaments obtained fibers ofdried graphene oxide. Several GO fibers were then immersed in a solutionof 10,12-pentacosadiyn-1-ol [CH₃(CH₂)₁₁C≡C—C≡C(CH₂)₈CH₂OH], or PCO,allowing PCO to permeate into GO fibers and contacting therewith. Asillustrated in Scheme 3, FIG. 5(C), the fibers, after drying, wereexposed to UV light to provide fibers of PCO-GO sheets in which thediacetylene groups of PCO react by 1,4-addition polymerization.Subsequently, the fibers were immersed in hydroiodic acid (HI) to reducethe PCO-GO sheets in the fiber into graphene-PCO sheets. Then, thefibers of graphene-PCO sheets is immersed successively into1-pyrenebutyric acid N-hydroxysuccinimide ester (PSE) and 1-aminopyrene(AP) solutions, thereby providing fibers of interconnected rGO sheets inwhich the PSE and AP have bonded through π-π interactions withneighboring rGO sheets and react to provide PSE-AP covalent bonds.

Multiple graphene fibers produced were made into yarns and fabrics. Someof the fabrics, the yarns, or the continuous/long graphene fibers weremade to have a cross-section that is rectangular or flat-shaped.Preferably, the graphene fibers were produced to have awidth-to-thickness ratio from 5 to 200. Some of the fabrics had athickness from 100 nm to 1 μm, and some from 1 μm to 100 μm. It may benoted that conventional continuous graphitic fiber yarns cannot be madeinto a fabric having a thickness less than 10 μm or less than 1 μm.

Example 4: Preparation of Graphene Fibers from Graphene Fluoride

Several processes have been used by us to produce graphene fluoride, butonly one process is herein described. In a typical procedure, highlyexfoliated graphite (HEG) was prepared from intercalated compoundC₂F.xClF₃. HEG was further fluorinated by vapors of chlorine trifluorideto yield fluorinated highly exfoliated graphite (FHEG). Pre-cooledTeflon reactor was filled with 20-30 mL of liquid pre-cooled ClF₃, thereactor was closed and cooled to liquid nitrogen temperature. Then, nomore than 1 g of HEG was put in a container with holes for ClF₃ gas toaccess and situated inside the reactor. In 7-10 days a gray-beigeproduct with approximate formula C₂F was formed.

Subsequently, a small amount of FHEG (approximately 0.5 mg) was mixedwith 20-30 mL of an organic solvent (methanol, ethanol, 1-propanol,2-propanol, 1-butanol, tert-butanol, isoamyl alcohol) and subjected toan ultrasound treatment (280 W) for 30 min, leading to the formation ofhomogeneous yellowish dispersions. Five minutes of sonication was enoughto obtain a relatively homogenous dispersion, but longer sonicationtimes ensured better stability. Upon extrusion to form filaments on aglass surface with the solvent removed, the dispersion became brownishfilaments formed on the glass surface.

Example 5: Preparation of Graphene Fibers from Nitrogenated Graphene

Graphene oxide (GO), synthesized in Example 2, was finely ground withdifferent proportions of urea and the pelletized mixture heated in amicrowave reactor (900 W) for 30 s. The product was washed several timeswith deionized water and vacuum dried. In this method graphene oxidegets simultaneously reduced and doped with nitrogen. The productsobtained with graphene/urea mass ratios of 1/0.5, 1/1 and 1/2 aredesignated as NGO-1, NGO-2 and NGO-3 respectively and the nitrogencontents of these samples were 14.7, 18.2 and 17.5 wt % respectively asfound by elemental analysis. These nitrogenated graphene sheets remaindispersible in water. The resulting suspensions were then extruded andmade into filaments. Upon drying, the resulting nitrogenated graphenefibers exhibit physical densities from 1.75 to 2.05 g/cm³.

Example 6: Chemical Functionalization of Graphene Fluoride andNitrogenated Graphene

Specimens of graphene fluoride fibers and nitrogenated graphene fibersprepared earlier were subjected to functionalization by bringing thesespecimens in chemical contact with chemical compounds such as carboxylicacids, azide compound (2-azidoethanol), alkyl silane, diethylenetriamine(DETA), and chemical species containing hydroxyl group, carboxyl group,amine group, and sulfonate group (—SO₃H) in a liquid or solution form.

Scanning electron microscopy (SEM), transmission electron microscopy(TEM) pictures of lattice imaging of the graphene filament, as well asselected-area electron diffraction (SAD), bright field (BF), anddark-field (DF) images were also conducted to characterize the structureof graphene fibers.

A close scrutiny and comparison of FIG. 3(a) indicates that the grapheneplanes in a graphene long fiber are substantially oriented parallel toone another; but this is not the case for coagulation-derived graphenefibers (FIG. 2(c)). The inclination angles between two identifiablelayers in the graphene fiber are mostly less than 5 degrees. Incontrast, there are so many folded graphene sheets, kinks, pores, andmis-orientations in coagulation-derived graphene fibers.

Examples 7: Electrical and Thermal Conductivity Measurements of VariousGraphene Fibers

Four-point probe tests were conducted on chemically functionalizedgraphene-derived fibers and coagulation-derived graphene fibers tomeasure their electrical conductivity. Their axial thermal conductivitywas measured using a laser flash method (Netzsch Thermal DiffusivityDevice). In order to obtain axial thermal conductivity, fibers ofapproximately 10 mm in width were stacked, laminated, and sectionedtransverse to the length of the fibers prior to measurement.

Due to the unique compositional and structural features, the presentlyinvented long or continuous fibers have a thermal conductivity typicallyfrom 200 to 1,600 W/mK. The electrical conductivity is typically from600 to 15,000 S/cm. These fibers have a thermal conductivity moretypically from 350 to 1,500 W/mK or an electrical conductivity moretypically from 1,000 to 12,000 S/cm.

Examples 8: Tensile Strength of Various Graphene Fibers

A universal testing machine was used to determine the tensile strengthand Young's modulus of various graphene fibers. Representative resultson tensile strength and Young's modulus for two types of presentlyinvented graphene-based continuous fibers and one conventional reducedgraphene oxide fiber are shown in FIG. 6. This specimen of a graphenefiber produced from chemically functionalized graphene sheets exhibits atensile strength of 2.26 GPa and a Young's modulus of 31 GPa. Thegraphene fiber produced from oriented GO sheets exhibits a tensilestrength of 2.0 GPa and Young's modulus of 60 GPa. Most of the presentlyinvented graphene fibers have a Young's modulus from 20 GPa to 300 GPa(more typically from 30 GPa to 150 GPa), or a tensile strength from 1.0GPa to 5.0 GPa (more typically from 1.2 GPa to 3.0 GPa).

We claim:
 1. A fabric comprising multiple yarns combined to form the fabric wherein at least one of said yarns comprises one or a plurality of graphene-based long or continuous fibers, wherein said graphene-based long or continuous fiber comprises chemically functionalized graphene sheets that are chemically bonded or interconnected with one another having an inter-planar spacing d₀₀₂ from 0.36 nm to 1.5 nm as determined by X-ray diffraction and a non-carbon element content of 0.1% to 47% by weight, wherein said functionalized graphene sheets are substantially parallel to one another and parallel to a fiber axis direction and said fiber contains no core-shell structure, has no helically arranged graphene domains, and has a length no less than 0.5 cm and a physical density from 1.5 to 2.25 g/cm³, wherein said functionalized graphene sheets are interconnected with one another via chemical bonding or reactions between chemically active functional groups attached to respective adjacent functional groups in a face-to-edge manner and an edge-to-edge manner, wherein the graphene-based long or continuous fiber comprises a combination of sp² and sp³ electronic configurations.
 2. The fabric of claim 1, wherein the fabric, the yarn, or the graphene-based long or continuous fiber has a cross-section that is rectangular or flat-shaped, having a width and a thickness.
 3. The fabric of claim 2, wherein the fabric, the yarn, or the graphene-based long or continuous fiber has a width-to-thickness ratio greater than
 5. 4. The fabric of claim 1, wherein the fabric or a yarn has a thickness less than 1 μm.
 5. The fabric of claim 1, wherein the fabric or a yarn has a thickness less than 100 nm.
 6. The fabric of claim 1, wherein the yarn has a packing factor greater than 60%.
 7. The fabric of claim 1, wherein the yarn has a packing factor greater than 70%.
 8. The fabric of claim 1, wherein the yarn has a packing factor greater than 80%.
 9. The fabric of claim 1, wherein said chemically functionalized graphene sheets comprise: (a) an oxygenated chemical functional group selected from the group consisting of hydroxyl, peroxide, ether, keto, aldehyde, and combinations thereof; (b) a chemical functional group selected from the group consisting of alkyl or aryl silane, alkyl or aralkyl group, hydroxyl group, carboxyl group, carboxylic group, amine group, sulfonate group (—SO₃H), aldehydic group, quinoidal, fluorocarbon, derivatives thereof, and combinations thereof; (c) a chemical functional group selected from the group consisting of 10,12-pentacosadiyn-1-ol, hydroiodic acid, 1-pyrenebutyric acid N-hydroxysuccinimide ester, 1-aminopyrene, derivatives thereof, and combinations thereof; or (d) a chemical functional group selected from the group consisting of amidoamines, polyamides, aliphatic amines, modified aliphatic amines, cycloaliphatic amines, aromatic amines, anhydrides, ketimines, diethylenetriamine (DETA), triethylene-tetramine (TETA), tetraethylene-pentamine (TEPA), polyethylene polyamine, polyamine epoxy adduct, phenolic hardener, non-brominated curing agent, non-amine curatives, derivatives thereof, and combinations thereof.
 10. The fabric of claim 1, wherein said chemically functionalized graphene sheets comprise a chemical functional group selected from a derivative of an azide compound selected from the group consisting of 2-azidoethanol, 3-azidopropan-1-amine, 4-(2-azidoethoxy)-4-oxobutanoic acid, 2-azidoethyl-2-bromo-2-methylpropanoate, chlorocarbonate, azidocarbonate, dichlorocarbene, carbene, aryne, nitrene, (R-)-oxycarbonyl nitrenes, where R=any one of the following groups,

and combinations thereof.
 11. The fabric of claim 1, wherein said chemically functionalized graphene sheets comprise a chemical functional group selected from the group consisting of —SO₃H, —COOH, —NH₂, —OH, —R′CHOH, —CHO, —CN, —COCl, halide, —COSH, —SH, —COOR′, —SR′, —SiR′₃, —Si(—OR′—)_(y)R′_(3-y), —Si(—O—SiR′₂—)OR′, —R″, Li, AlR′₂, Hg—X, TlZ₂ and Mg—X; wherein y is an integer equal to or less than 3, R′ is hydrogen, alkyl, aryl, cycloalkyl, or aralkyl, cycloaryl, or poly(alkylether), R″ is fluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl or cycloaryl, X is halide, and Z is carboxylate or trifluoroacetate, derivatives thereof, and combinations thereof.
 12. The fabric of claim 1, wherein said chemically functionalized graphene sheets comprise a chemical functional group selected from OY, NHY, O═C—OY, P═C—NR′Y, O═C—SY, O═C—Y, —CR′1-OY, N′Y or C′Y, a derivative thereof, or a combination thereof, and Y is a functional group of a protein, a peptide, an amino acid, an enzyme, an antibody, a nucleotide, an oligonucleotide, an antigen, or an enzyme substrate, enzyme inhibitor or the transition state analog of an enzyme substrate or is selected from R′—OH, R′—NR′₂, R′SH, R′CHO, R′CN, R′X, R′N⁺(R′)₃X⁻, R′SiR′₃, R′Si(—OR′—)_(y)R′_(3-y), R′Si(—O—SiR′₂—)OR′, R′—R″, R′—N—CO, (C₂H₄O—)_(w)H, (—C₃H₆O—)_(w)H, (—C₂H₄O)_(w)—R′, (C₃H₆O)_(w)—R′, R′, and w is an integer greater than one and less than
 200. 13. The fabric of claim 1, wherein said inter-plane spacing d₀₀₂ is from 0.4 nm to 1.2 nm, the non-carbon element content is from 1% to 20%, or physical density from 1.7 to 2.15 g/cm³.
 14. The fabric of claim 1, wherein the graphene-based long or continuous fiber has a cross-section that is circular, elliptical, rectangular, flat-shaped, or hollow.
 15. The fabric of claim 1, wherein the graphene-based long or continuous fiber has a length from 1 cm to 10,000 meters, a cross-section having a width or second largest dimension from 1 μm to 5 mm, and a thickness or smallest dimension from 10 nm to 500 μm, and a width-to-thickness ratio from 1 to 10,000.
 16. The fabric of claim 1, wherein the graphene-based long or continuous fiber has a thickness from 100 nm to 100 μm.
 17. The fabric of claim 1, wherein the graphene-based long or continuous fiber has a thermal conductivity from 200 to 1,600 W/mK, or an electrical conductivity from 600 to 15,000 S/cm.
 18. The fabric of claim 1, wherein the graphene-based long or continuous fiber has a thermal conductivity of at least 350 W/mK, or an electrical conductivity no less than 1,000 S/cm.
 19. The fabric of claim 1, wherein the graphene-based long or continuous fiber has a thermal conductivity of at least 600 W/mK, or an electrical conductivity no less than 2,500 S/cm.
 20. The fabric of claim 1, wherein the graphene-based long or continuous fiber has a thermal conductivity of at least 1,000 W/mK, or an electrical conductivity no less than 5,000 S/cm.
 21. The fabric of claim 1, wherein the graphene-based long or continuous fiber a thermal conductivity of at least 1,200 W/mK, or an electrical conductivity no less than 8,000 S/cm.
 22. The fabric of claim 1, wherein the graphene-based long or continuous fiber has a degree of orientation from 86% to 99%.
 23. The fabric of claim 1, wherein the graphene-based long or continuous fiber has a Young's modulus from 20 GPa to 300 GPa or a tensile strength from 1.0 GPa to 5.0 GPa.
 24. The fabric of claim 1, wherein the graphene-based long or continuous fiber has a Young's modulus from 30 GPa to 150 GPa or a tensile strength from 1.2 GPa to 3.0 GPa. 